Telecentric lens system for providing an image with the principal rays parallel to the optical axis and normal to the focal plane

ABSTRACT

A LENS SYSTEM WHICH MAGNIFIES AN INCIDENT IMAGE FIVE TIMES AND CAUSES THE LIGHT LEAVING THE LENS SYSTEM TO BE SUBSTANTIALLY PARALLEL SO AS TO PERMIT PERPENDICULAR IMPINGEMENT UPON A DEVICE SUCH AS A PLANE MATRIX SITUATED AT THE LOCAL PLANE OF THE LENS SYSTEM.

Feb. 23, 1971 o. c. DILWORTH 3,565,511 TELECENTRIC mans SYSTEM FOR PROVIDING AN IMAGE WITH THE A PRINCIPAL RAYS PARALLEL TO THE OPTICAL AXIS AND NORMAL TO THE FOCAL PLANE Filed April 23, 1969 INVENTOR Fa/v 1721 h/ae/A I NxY Q W W N w A. x w W W m r W r b v 3 Q Q ew m d \\W-\ KN y W \Q N.\ N N m N Nh b N\ NN Q A \N Q RQ United States Patentus. or. 350-176 1 Claims ABSTRACT OF THE DISCLOSURE A lens '-systemwhichmagnifiesan incident image five times and causes the light leaving the lens system to be "substantially parallel so as to permit perpendicular impingement upon a device such as a plane' matrix situated at thefocal plane of the lens system.

BRIEF DESCRIPTION OF THE PRIOR ART ANDSUMMARY or THE INVENTION time insure that the light leaving the lens system as that magnified ,image is substantially parallel and perpendicular to some plane, for example, the focal plane of the" system. .This requirement is particularly present when, the image is to be impinged upon a matrix of phototransistors or like elements, since such devices are usually sensitive to the angle to which the light enters the phototransistor. If such a transistor is being used to indicate an on or off conditon in response to a given threshold valuerof impinging light, any variation in entrant angle may severely effect the actual threshold value and thus cause whatever logical .or other apparatus attached to the matrix to respond or not to respond incorrectly.

Thus, it is important that the light which impinges upon such phototransistors or like elements enter at substantially 90 to the phototr'ansistor or like device. Unfortunately, conventional lens arrangements while capable of performing the magnification which is frequently necessary with such an arrangement, also unfortunately may produce a diverging image which will not enter exactly perpendicularly for some-of the transistors and the entrant angle will vary over the matrix with the undesirable results described briefly above. In the present invention, this problem is solved by a simple arrangement of optical elements, which not only performs the five fold magnification required, but also produces a magnified image comprised of substantially parallel light so that if a photo-transistor matrix or similar .device is placed at the focal plane. of the system as described below, the light will enter each and every phototransistor at substantially 90 to that phototransistor and problems attendant upon non-parallel entrance are substantially eliminated.

The exact unique configuration .for performing this function is described in detail below and is comprised "ice of a plurality of simple lenses of the described type and arrangement which operated to magnify the image to the desired size and also to render the light parallel. Many other objects and purposes of the invention will 5 become clear from reading the following detailed dedescription of the drawing. I

BRIEF DESCRIPTION OF THE DRAWING The figure shows a lens arrangement together with a photodetector matrix.

DETAILED DESCRIPTION OF THE DRAWING 7 Reference is now made to FIG. 1 which shows the unique combination of lens elements 16 which results in the novel capability of thissystem, as discussed above, to magnify an incident image transmitted through the combination 16 along an optical axis 18 five times, while at the same time rendering the light" comprising that magnified output image substantially parallel.

20 The incident image, which may come from any suitable source and may be of any suitable size such as to be magnified by the lenses shown, is first'incident upon a first cylindrical lens 20 through which'it passes to a second cylindrical lens 22 which is disposed with 25 its axis at a substantially right angle to the -,lens 20.

' Next, the image travels from lens' 22 a distance S to a prism 24 of thickness t and through it 'to'a biconvex lens 26 separated from the surface R of prism 24 by distance S Lens 26 has a surface K; through which the light enters, a thickness t an a surface R through which the light exits. The light exiting from surface R travels a distance 8, and next passes through another biconvex lens 28 having surfaces R and R. and a thickness 1,; to a biconcave'lens 30 having surfaces 'R and R1 and thickness tgLens 30 is separated from lens 28 by 'a distance 5: as shown which is virtually zeros'oth at lenses 30 and 28 are in contact. Next, the lighf exiting from lens'30 travels distance S to concave-convex lens 32 having concave surface R and convex surface R 40 as well as a thickness 1 Finally, the light travels a distance S to a convex lens 34 having surfaces R and R and thickness t and thenthrough a lens 38 with surfaces R and R and thickness 1 to a diode photo-transistor or photodetector matrix 42.disposed at the focal plane of the system and separated from surface R by distance It.will of course be appreciated that the unique advantages of this system have been achieved by a judicious combination of lens parameters and arrangements chosen by computation and experimentation. It will further be appreciated that for any given constructed system, the values given below, which represent whatis believed to be the optimum values, may be varied slightly to compensatefor imperfect lenses or. for any other reason. Moreover, his not "the exact sizes and physical distances which result in the advantages of: this system but rather the relation of the sizes, characteristics and separations of the various lenses comprising the system which produces the novel results. Accordingly, it should be apparent that such sizes, characteristics and separations can -be easily varied provided that each lens is varied proportional to each other lens. with their relation to each other remaining the same. The following Table 65 I gives the thicknesses and separations of the lenses in inches for one constructed embodiment measured along theoptical axis 18. These values can be multiplied by any number, integer or non-integer.

Moreover the lenses in the embodiment constructed had radii of curvature and diameters expressed in inches as follows in Table II with concavesurfaces designated by a minus sign:

TABLE H R =oo (Diameter Lens 26:0.447) R3=OO (Diameter Lens 28:0.447) R =1.148 (Diameter Lens 30=0.447) R =0.256 (Diameter Lens 32:0.600) R =0.444 (Diameter Lens 34=1.400) R =-0.598 (Diameter Lens 38=2.425) R-,=0.488

Even further the glasses in the lenses in the constructed embodiment had indexes of refraction, Abbe numbers (absolute values), clear apertures and glasses as follows in Tables III, IV, V and VI:

TABLE III.N

d Prism 24 1.62374 Lens 26 1.85026 Lens 28 1.72000 Lens 30 1.76180 Lens 32 1.85026 Lens 34 1.57250 Lens 38 1.62374 TABLE IV.V d Prism 24 47.00 Lens 26 32.23 Lens 28 50.41 Lens 30 26.95 Lens 32 32.23 Lens 34 57.55 Lens 38 47.00

TABLE V.Clearance App.

Cl. Ap. Lens 26:

Surface R 0.374 Surface R4 Lens 28:

Surface R 0.309 Surface R 0.177 Lens 30: Surface R 0.177 Surface R 0.107 Lens 32:

Surface R 0.420 Surface R 0.538 Lens 34:

SurfaceR 1.200 Surface R 1.250 Lens 38:

Surface R 2.360 Surface R 2.360

TABLE VL-GlaSs Many modifications and changes of the above embodiment can of course be made without departingfroin the" s'piritof the inve'hfion andaccordingly the,s cope of the invention is intended to. be limited onlyiby the scope of the appended claims. J I

What is claimed is: I

1. An optical system which is telecentric on the image side with the principal rays parallel to the optical axis and normal to the focal plane for magnifying an entrant image five times comprising:

a prism for receiving the entrant image and having a thickness t along the optical axis,

a first lens disposed rearwardly of said prism having a thickness 1, along the optical axis, a first convex surface R facing and separated from said prism by a distance S along the optical axis and a second convex surface R a second lens disposed rearwardly of said first lens having a thickness i along the optical axis, a first convex surface R facing said surface R and separated from said surface R; by a distance 8; along the optical axis and a second convex surface R,,

a third lens disposed rearwardly of said second lens having a thickness 1 along the optical axis, a first concave surface R in contact with said surface R and a second concave surface R a fourth lens disposed rearwardly of said third lens having a thickness 1 along the optical axis, a first concave surafce R facing said surface R and separated from said surface R-; by a distance S along the optical axis, and a second convex surface 11,,

a fifth lens disposed rearwardly of said fourth lens having a thickness t,, a first convex surface R facing and separated from said surface R, by a distance S along the optical axis and a second convex surface a sixth lens disposed rearwardly of said fifth lens having a thickness t a first convex surface R facing and separated from said surface R by a distance S along the optical axis, and a second flat surface R and the relative values of the thicknesses and distances with respect to the other thicknesses and distances being approximately S1= .070 tz=0.075

S =0.219 t4 0.068 I all ' said "fifihlens has an absolute refraction index of i approximately 1.57250, an absolute Abbe number of approximately $7.55 and a diameter of approximately said sixth lens has an absolute refraction index of approximately 1.62374, an absolute .Abbe number of approximately 47.00 and a diameter of approximately 2.425, and

the values 'of said diameters are relative to each other.

3. A system as in claim 2 wherein said prism is comprised of glass BAP-8,

said first lens is comprised of glass LASF-9,

said second lens is comprised of glass LAX-10,

said third lens is comprised of glass SF-55,

said fourth lens is comprised of glass LASF-Q,

said fifth lens is comprised of glass BAK-l, and

said sixth lens is comprised of glass BAP-8.

4. A system as in claim 1 wherein:

said surface R, has a radius of curvature of approximately infinity,

said surface-R, has a radius of curvature of approximately infinity,

said surface R; has a radius of curvature of approximately 1.148 and a clear aperture of approximately 0.374;

said surface R, has a radius of curvature of approximately 0.25 6 and a clear aperture of approximately 0.362,

said surface R, has a radius of curvature of approximately 0.444 and a clear aperture of approximately 40 said surface R, has a radius of curvature of approximately 0. 598 and a clear aperture of approximately 0.177,

said surface R, has a radius of curvature of approximately 0.488 and a clear aperture of approximately 0.107,

said surface R, has a radius of curvature of approximately 0.810 and a clear aperture of approximately 0.420,

said surface R, has a radius of curvature of approximately 0.545 and a clear aperture of approximately 0.538,

said surface R has a radius of curvature of approximately 2.130 and a clear aperture of approximately 1.200,

M said surface R has aradius of curvature of approxi- 10 mate1y'- -3 .505 and a clear aperture of approximately said surface R has a radius, of curvature 'ofapproximately 3.015 (and a clear, aperture of approximately 2.360, I

said surface R has a radius of curvature of approxia concave surface and said values of radii of curva-.

ture and clear apertures are relative to the other values of radii and clear aperture respectively.

5. A system as in claim 1 including a matrix of light sensitive devices disposed to receive said magnified image comprised of substantially parallel light.

6. A system as in claim 5 wherein said matrix is located approximately on the focal plane of the system.

7. A system as in claim 1 further including a first cylindrical lens, a second cylindrical lens disposed rearwardly of said first cylindrical lens with its axis substantially perpendicular to the axis of said first cylindrical lens, said first and second cylindrical lenses being disposed so as to receive said entrant image and pass said entrant image to said prism and said second cylindrical lens being separated by a distance of approximately 0.3

along the optical axis from said prism relative to the values of separation and thickness of the other lenses and prism.

References Cited UNITED STATES PATENTS 2,651,970 9/1953 Tiller 350(175TS)UX 2,685,229 8/ 1954 Schulz et al. 350-(175TS)UX 3,278,752 10/1966 Brixner 350205X JOHN K. CORBIN, Primary Examiner U.S. Cl. X.R. 

